... is it really worth the bother ... for such minimal gains?
Back when I looked at Bifacial panels they were also "double glass", so extremely resistant to corrosion and had 30 year warranties that made me drool a little. So, even without power from the backside they might be warranted if they've comparable prices. I eventually bailed on the concept because I couldn't overcome the elevation issue... but these forums didn't exist back then, now people can get help for stuff like this.
it's probably not... the money I spend on extra racking etc would probably take years to make up in bi-facial gains....
I wouldn't be so sure!
At 12 cents a kwh, each 340 watt panel with an average insolation of 4, the savings per year per panel would be:
.12 $/kWh x .34 kW x 4 x 365 x Y% gain = 60 x Y%
| 10% | 20% | 30% | 40% |
Yearly $$ at Average | $6 | $12 | $18 | $24 |
Value $$ at 20 years | $120 | $240 | $360 | $480 |
$$ Saved 12 Panels @ 20 Years | $1440 | $2880 | $4320 | $5760 |
So, if it costs $12 more per panel with mounting hardware, even at 10% gain it pays itself back in two years.
Fine-Print: Assuming my calculator is correct....
... we over engineer and ... that's half the fun...
Amen!
What's to the north in this picture? Is the property surrounded by a brim like the one behind the shed? If so, you might be able to use the tilt of the brim for mounting similar to how Will mounts them flat on his driveway. A top-down google-earth type snapshot would be nice too.
While I love the idea of using the roof reflectivity, I can't help but wonder if some member might be able to look at the property and suggest an alternative where you can get the back-side to work for you without breaking the bank.
But I wouldn't give up on the shed either. Possibly it's strong enough, or possibly it can be reinforced? For example, when I lived in Colorado I sistered the rafters so the roof could take the weight for concrete tile and snow. Here in Florida a nearby house was retrofitted with hurricane tie-down straps just to get the insurance break (pays for itself in a few years and your roof is less likely to get sucked off).
So, possibly some pics of the shed's foundation, the wall members, and the roof supports? If the roofing members and wall studs are all still exposed in the shed it might be easy to reinforce them without any/much disassembling. Take a look at the "
hurricane strapping" article, it'll give you some ideas as to what to take photos of in the roofing.
How tough is it to get a building permit there? Here you can't do anything
alternative without a couple of engineering companies swearing to it and even then insurance won't touch it. But there are a lot places you can't even get a building permit/review if you want one. The reason I ask is that it might even be possible to build an elevated ground superstructure on the exterior of the shed that allows the panels to be over them and gives the needed support.
The community would need to know more about the local building codes though to help you with that, primarily wind and snow. You can find what the "hazards" (e.g., max wind speed, max snow load) are for your area
here.